There's fine line with buying the right player should the need to replace Shaw arise. For instance at Arsenal, they signed Andre Santos for 7 million, and for a similar price had to buy Monreal to replace him.
Good replacements are out there for Shaw though, which is why, as long as the price is right, I'm not too concerned with seeing him go. (As long as it's after the World Cup) Lallana though will be very difficult to replace satisfactorily, and given his longevity at the club already, I really want to see him stay.